Method and apparatus for making ammonium perchlorate

ABSTRACT

A method and apparatus for making finely particulate ammonium perchlorate by vapor phase reaction between gaseous ammonia and anhydrous perchloric acid vapor. The gaseous ammonia is preferably mixed with an inert carrier gas and the resulting mixture reacted with substantially pure, anhydrous perchloric acid vapor to form fine ammonium perchlorate particles. The ammonium perchlorate particles may be separated from the gas mixture by an electrostatic precipitator or by means of a spray tower.

nite States atent Guzzo [451 Dec.23,1975

METHOD AND APPARATUS FOR MAKING AMMONIUM PERCHLORATE Anthony T. Guzzo, Huntsville, Ala.

Thiokol Corporation, Bristol, Pa.

Dec. 11, 1970 Inventor:

Assignee:

Filed:

Appl. No.:

US. Cl. 423/476; 149/76 Int. Cl C01b 11/16 Field of Search 23/85; 149/76; 423/476 References Cited UNITED STATES PATENTS 3,728,169 4/1973 Diebold 423/476 X FOREIGN PATENTS OR APPLICATIONS 1,020,047 2/1966 United Kingdom 23/85 631,947 11/1961 Canada 23/85 OTHER PUBLICATIONS Schumacher, Perchlorates-Their Properties, Manufacture, and Uses, Reinhold Pub. Corp., N.Y., 1960, pp. 71, 99.

Primary Examiner-Benjamin R. Padgett Assistant Examiner-E. A. Miller [57] ABSTRACT A method and apparatus for making finely particulate ammonium perchlorate by vapor phase reaction be tween gaseous ammonia and anhydrous perchloric acid vapor. The gaseous ammonia is preferably mixed with an inert carrier gas and the resulting mixture re acted with substantially pure, anhydrous perchloric acid vapor to form fine ammonium perchlorate particles. The ammonium perchlorate particles may be separated from the gas mixture by an electrostatic precip itator or by means of a spray tower.

7 Claims, 1 Drawing Figure STEAM CONDENSATE SULFURlG ACID US. Pamnt Dec. 23, 1975 3,928,546

METHOD AND APPARATUS FOR MAKING AMMONIUM PERCHLORATE I This invention relates to the manufacture of ammobinder, and certain special purpose ingredients knownin theart are dispersed in the binder while the latter is in viscous fluid form; and the resulting mixture is cast in situ in a rocket motor casing at a temperature sufficient to convert the binder to elastorneric form.

It is known that the efficiency and rate of combustion of a solid propellant can be maximized by'increasing the area'of contact between the oxidizer and other ingredients of the propellant composition and that this area of contact can be increased by reducing the particle' size-of the oxidizer. Consequently, rocket propellant oxidizers, prior to their incorporation in the fuelbinder,'-have customarily been subjected to one or more mechanical grinding operations. However, such grinding operations are subject to a number of disadvantages. Thus they involve a considerable explosion hazard and numerous precautions must be taken to minimize the risk of explosion. Moreover, the risk of explosion can never be completely eliminated. Also there is a tendency for the ammonium perchlorate to become contaminated 'by material removed from the grinder and grinding media. In addition, grinding is a relatively expensive and time consuming procedure, and it has not been found possible to reduce the particle size of the oxidizer by grinding to the extent that it is desirable for highly efficient propellant combustion.

Because of the foregoing disadvantages various proposals have previously been made for producing finely particulate oxidizers other than by grinding. ThusU.S. Pat. No. 3,452,445 discloses a process for making fine particles ofammonium perchlorate by quick freezing of aqueous ammonium perchlorate. Freezing of the aqueous solution is effected by rapidly rotating a flask containing the solution in an acetone-dry ice bath.'The ice thus formed is then sublimed under a reduced pressure to recover ammonium perchlorate particles having an average size of 117 to 2.1 microns.

US. Pat. No. 3,222,231 discloses a process wherein a saturated aqueous solution of ammonium perchlorate at a temperature of 95C. is simultaneously agitated and subjected to ultra-sonic vibrations over a period of several hours. As the solution cools,ammonium perchlorate crystals precipitate and are subsequently removed from the solution, washed with acetone and ether and dried. The product crystals had a particle size within the range to350 microns.

While such processes avoid the explosion hazards involved in mechanical grinding, the size of the ammonium perchlorate particles they produce is of the same order of magnitude as, or in some cases larger than, that produced by the grinding process. It is accordingly an object of the present invention to provide a process for preparing ammonium perchlorate having an average particle size less than that provided by prior processes. lt is another object of the invention to provide a process for making ammonium perchlorate which eliminates the explosion hazard involved in the grinding operation referred to above. It is another object of the invention to provide a process for making ultra-fine ammonium perchlorate of high purity at a low unit cost. It is still another object of the invention to provide such a process that can be readily automated. It is a still further object of the invention to provide a process wherein for any given production rate the quantity of material being processed is relatively small. It is still another object of the invention to provide apparatus for carrying out the method of the invention. Other objects of the invention will be in part obvious and in part pointed out hereafter.

The objects of the invention are achieved, in general, by a direct addition reaction of gaseous ammonia and substantially anhydrous perchloric acid vapor according to the following equation:

Nl-l +HCIO4 -v NH4CIO4 The gaseous ammonia is preferably incorporated in an inert carrier gas and the ammonia-containing carrier gas is mixed with substantially pure, anhydrous perchloric acid to form a suspension of fine ammonium perchlorate particles in the carrier gas. The relative proportions of gaseous ammonia and anhydrous perchloric acid used are preferably such that there is a small excess, say about 5 to 10 weight percent, of ammonia to ensure rapid and complete reaction of the perchloric acid when it is mixed with the ammonia containing carrier gas.

The anhydrous perchloric acid can be conveniently pi'epared by mixing an aqueous perchloric acid, containing say percent by weight of the acid, with fuming sulfuric acid as illustrated by the following equation:

HClO .2H O [0 H2804 2 HClO When such a mixture is heated at a reduced pressure of say 1 mm. of Hg, anhydrous perchloric acid is vaporized therefrom. When operating on a batch basis, it is necessary to increase the temperature to which the mixture is heated as perchloric acid is vaporized therefrom. For example, at the indicated pressure of 1 mm. of Hg the temperature in the perchloric acid generator may vary from say- 25C. to C.

The diluent or carrier gas used incarrying out the process of the invention should be inert to the reactants and any of various gases may be used for this purpose. Suitable gases include nitrogen, helium, symmetrical difluorotetrachloroethane (Freon l 13) and air. The concentration of ammonia in the diluent gas is not critical and may vary from say l to 10 percent by volume. v

The reaction between the ammonia and perchloric acid to form a suspension of fine ammonium perchlorate in the carrier gas is exothermic and the suspension is desirably cooled before removal of the ammonium perchlorate particles therefrom. Separation of the particles may be effected by means of an electrostatic precipitator, or alternatively, in a spray tower wherein the suspension is caused to flow countercurrently to a spray of a suitable liquid, e.g., Freon 11 3. The liquid medium used to collect the particles can be either completely evaporated to recover the ammonium perchlorate in dry powder form or partially evaporated to form a paste which, in cases where the ammonium perchlorate is to be used in a propellant, can be transferred to the propellant mixer.

In order to point out more fully the nature of the present invention, reference will now be made to the accompanying drawing which shows diagrammatically an illustrative system for carrying out the process of the invention. Referring to the drawing, the system there shown is a semi-batch embodiment of the process in that batch-wise generation of the perchloric acid is used in conjunction with continuous flow of the ammonia and carrier gas. However, it will be apparent that the system can be readily modified for fully continuous operation.

In the drawing the numeral designates a perchloric acid generator which is charged with aqueous perchloric acid of 72 percent concentration and percent fuming sulfuric acid through a pipe 12 containing a valve 14. The generator 10 is provided with a heating coil 16 supplied with steam through a pipe 18 and condensate is removed through pipe 20. Perchloric acid vaporized in generator 10 flows through a pipe 22 containing an orifice plate 24 and control valve 26 to the neck portion of an ejector or venturi tube 28. The pressure within generator 10 is maintained constant by an automatic controller 30 made responsive to the pressure in the generator 10 through a pipe 32 and producing a pneumatic pressure transmitted through pipe 34 to control valve 26.

In the system shown in the drawing the carrier gas is recirculated in a closed cycle and the ammonia gas is continuously added thereto. More particularly, gaseous ammonia from a suitable source enters the system through a pipe 36, is mixed with recycled carrier gas flowing through pipe 38 and the resulting mixture flows through pipe 40 to the inlet of ejector 28. Connected to pipe 38 there is inert gas supply pipe 42 containing a valve 44 for supplying make-up carrier gas to the system when and as required.

The ejector 28 performs two functions. The gas mixture entering the ejector through pipe 40 is a working fluid that produces a reduced pressure at the neck of the ejector and thereby maintains a reduced pressure in the perchloric acid generator 10. Also the ejector acts as a reaction chamber wherein the ammonia and perchloric acid are mixed and reacted to form ammonium perchlorate particles. In order to achieve the desired relatively low pressure at the neck of ejector 28, the gas supplied to the inlet of the ejector through pipe 40 should be at a relatively high pressure, say 100 to 300 p.s.i. and in sufficient volume to produce the desired pressure reduction at the neck of the ejector.

The relative proportions of perchloric acid and ammonia fed to ejector 28 are controlled by means of a flow controller 46 which is made responsive to the differential pressure across orifice plate 24 through pipe 48 and generates a pneumatic signal transmitted through pipe 50 to a control valve 52 in the ammonia inlet pipe 36. As indicated above, the ammonia is preferably used in an amount that is stoichiometrically in excess of that required for reaction with the perchloric acid and the controller 46 is adjusted to provide this excess.

From ejector 28 the carrier gas and suspended perchlorate particles flow through a pipe 54 to a cooler 56 supplied with cooling water through a pipe 58 and thence through a pipe 60 to an electrostatic precipitator 62. In the precipitator 62 the ammonium perchlorate particles are separated from the carrier gas and flow through pipe 64 to a collector tank 66. The carrier gas leaves the precipitator through a pipe 68 and flows to a compressor 70 wherein it is compressed to the injector inlet pressure referred to above. From compressor 70 the gas flows through pipe 72 to a cooler 74 supplied with cooling water through a pipe 76 and thence through pipes 38 and 40 back to ejector 28.

Since the ammonia and anhydrous perchloric acid react on a mole for mole basis, the quantities to be used can be readily determined. For example, to produce pounds per day of ammonium perchlorate particles (45,400 grams per day), the perchloric acid generator 10 would be operated at such a temperature and pressure as to vaporize 27 grams per minute of anhydrous perchloric acid. Assuming that nitrogen is used as the carrier gas a suitable gas flow would be 600 grams per minute containing about 5 grams per minute of ammonia. With these flows about 31.5 grams per minute of ammonium perchlorate particles would be produced.

The temperature and pressure at which precipitator 62 is operated are not critical. The precipitator can conveniently be operated at ambient temperatures and at a pressure at or slightly above atmospheric pressure. In cases where a spray tower is used in place of the precipitator, the operating temperature may be above or below ambient temperature depending upon the volatility of the liquid medium used to remove the particles from the carrier gas.

It is, of course, to be understood that the foregoing description is illustrative only and that numerous changes can be made in the materials, proportions and conditions given above without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. The method of making ammonium perchlorate which comprises causing a stream of inert gas to flow in a closed cycle, adding gaseous ammonia to said inert gas stream at a first point in said cycle, adding substantially anhydrous perchloric acid vapor to said stream at a second point in said cycle to cause said perchloric acid vapor to react with said ammonia to form finely particulate ammonium perchlorate particles, and separating said ammonium perchlorate particles from said stream at a third point in said cycle.

2. A method according to claim 1 wherein said ammonia and perchloric acid are added to said stream at rates such that the ammonia is in stoichiometric excess of that required to react with the perchloric acid.

3. A method according to claim 1 wherein said gas stream is cooled between said second and third points in said cycle.

4. A method according to claim 1 wherein said particulate ammonium perchlorate is removed from said stream by electrostatic precipitation.

5. A method according to claim 1 wherein said particulate ammonium perchlorate is removed from said stream by a liquid spray.

6. A method according to claim 1 wherein said stream is passed through an ejector at said second point in said cycle and thereby draws said perchloric acid vapor into said stream.

7. A method according to claim 1 wherein said gas stream is compressed and cooled between said third and first points in said cycle. 

1. THE METHOD OF MAKING AMMONIUM PERCHLORATE WHICH COMPRISES CAUSING A STREAM OF INERT GAS TO FLOW IN A CLOSED CYCLE, ADDING GASEOUS AMMONIA TO SAID INERT GAS STREAM AT A FIRST POINT IN AID CYCLE, ADDING SUBSTANTIALLY ANHYDROUS PERCHLORIC ACID VAPOR TO SAID STREAM AT A SECOND POINT IN SAID CYCLE TO CAUSE SAID PERCHLORIC ACID VAPOR TO REACT WITH SAID AMMONIA TO FORM FINELY PARTICULATE AMMONIUM PERCHLORATE PARTICLES, AND SEPARATING SAID AMMONIUM PERCHLORATE PARTICLES FROM SAID STREAM AT A THIRD POINT IN SAID CYCLE.
 2. A method according to claim 1 wherein said ammonia and perchloric acid are added to said stream at rates such that the ammonia is in stoichiometric excess of that required to react with the perchloric acid.
 3. A method according to claim 1 wherein said gas stream is cooled between said second and third points in said cycle.
 4. A method according to claim 1 wherein said particulate ammonium perchlorate is removed from said stream by electrostatic precipitation.
 5. A method according to claim 1 wherein said particulate ammonium perchlorate is removed from said stream by a liquid spray.
 6. A method according to claim 1 wherein said stream is passed through an ejector at said second point in said cycle and thereby draws said perchloric acid vapor into said stream.
 7. A method according to claim 1 wherein said gas stream is compressed and cooled between said third and first points in said cycle. 